Due to the high concentration of nitrification-inhibiting toxic materials in coking-plant wastewater from a coking-plant, it is among the most problematic of all industrial wastewater. For treatment with conventional biological methods, low-load, and therefore large-volume, bioreactors of a basin-type construction are necessary. Sensitive biological processes, for example nitrification, are always at risk of succumbing to sudden loads involving critical substances, such as cyanide and phenol. By dividing the treatment into a first biological step for degrading organic compounds, hydrolysis and denitrification and a second nitrification step, as well as by connecting these two steps by recycling nitrates, the space requirements for the bioreactors are reduced, and sensitive, slow-growing autotrophic bacteria are protected against harm from cyanide, phenol and other toxic agents.
Nevertheless, the needed space requirements as well as the sheer size of the concrete structures for this process are extraordinarily great, and therefore extremely costly. Due to spatial restrictions that are frequently encountered in coking plants, the described wastewater treatment method is not suited for use in existing coking plants.
DE 103 18 736 [US 2007/0012619] discloses a method of treating the wastewater from coking plants that provides for the untreated wastewater to flow through a reactor incorporated in fluid circulation path and that contains membrane tubes that are gas-permeable, with an oxygen-containing gas flowing in and through them. A biofilm is maintained on the exterior of the membrane tubes bathed in fluid flowing there-around and is where a selective nitrification of nitrogen-containing compounds contained in the wastewater into nitrates occurs; plus, simultaneously, a denitrification of nitrates into elementary nitrogen occurs in an oxygen-poor outer area of the biofilm. This method has not been successful in practice. The formation and maintenance of the defined biofilm have proved difficult. Moreover, providing the necessary exchange areas for nitrification and denitrification on the membrane surfaces has proved difficult.
DE 198 42 332 discloses a method of biologically treating wastewater that uses a reactor including a gas-exposure zone for introducing a gaseous oxidizing agent into the untreated fluid and/or for the optimal supply of the biomass with wastewater, as well as a reaction zone for degrading pollutants. The fluid mixture is returned from the reaction zone to the gas-exposure zone and reconcentrated there with gas and substrate. This method provides for a strict separation between the gas-exposure zone where the gas is introduced into the fluid and mixed therewith and the reaction zone where the pollutants are biologically degraded. The method can be used for the biological treatment of municipal wastewater. In the case of treating wastewater from coking plants, the problem still remains that the coking-plant wastewater is loaded with pollutants that inhibit nitrification.